refactor(zone): remove legacy route domain storage

第二阶段清理：删除 of_managed_domains 与 of_proxy_routes 冗余域名/证书列，
移除 ManagedDomain 模型与 API、路由侧 legacy 字段维护，以及前端 WebsiteService。
ImportLegacy 在旧列/旧表缺失时跳过对应源，保持幂等。

internal/apps/openflare/proxy_route/logics.go

@@ -5,7 +5,6 @@ package proxy_route
 
 import (
 	"context"
-	"encoding/json"
 	"errors"
 	"strings"
 	"time"
@@ -253,43 +252,12 @@ func buildProxyRoute(ctx context.Context, route *model.ProxyRoute, input Input)
 		limitRate,
 		upstreamType,
 	)
-	// Preserve legacy columns until the second-phase schema cleanup. They are
-	// derived solely from ZoneDomain bindings and are not exposed by this API.
-	populateLegacyZoneDomainFields(route, domains)
 	if err := applyProxyRouteUpstreamType(ctx, route, upstreamType, input); err != nil {
 		return nil, nil, err
 	}
 	return route, domains, nil
 }
 
-func mustMarshalProxyRouteLegacy(value any) string {
-	encoded, err := json.Marshal(value)
-	if err != nil {
-		panic(err)
-	}
-	return string(encoded)
-}
-
-func populateLegacyZoneDomainFields(route *model.ProxyRoute, domains []model.ZoneDomain) {
-	legacyDomains := make([]string, 0, len(domains))
-	legacyCertIDs := make([]uint, 0, len(domains))
-	for _, domain := range domains {
-		legacyDomains = append(legacyDomains, domain.Domain)
-		if domain.CertID != nil {
-			legacyCertIDs = append(legacyCertIDs, *domain.CertID)
-		}
-	}
-	route.Domain = legacyDomains[0]
-	route.Domains = mustMarshalProxyRouteLegacy(legacyDomains)
-	route.CertIDs = mustMarshalProxyRouteLegacy(legacyCertIDs)
-	if len(legacyCertIDs) > 0 {
-		route.CertID = &legacyCertIDs[0]
-	} else {
-		route.CertID = nil
-	}
-	route.DomainCertIDs = route.CertIDs
-}
-
 func buildProxyRouteViews(ctx context.Context, routes []*model.ProxyRoute) ([]*View, error) {
 	views := make([]*View, 0, len(routes))
 	for _, route := range routes {